Diaphragm pushbutton switches

ABSTRACT

Pushbutton diaphragm switches are provided. Switch contacts in a hermetically sealed environment are energized by changes in magnetic fields caused by motion of a permanent magnet under control of a pushbutton. A pushbutton spring may be dispensed with and magnetic attraction may be relied upon to provide the necessary restoring force.

United States Patent 1111 3,582,596

I 72] Inventor Harry Stanley Woodhead [56] References Cited Harlow, England UNITED STATES PATENTS QY J' 3 1969 3,005,055 10/1961 Mattke 200/6AX [22] 3,331,040 7/1967 Woodhead. 335 196x [45] Patented June I, 1971 73 A [me ls d kc 3,465,271 9/1969 Koepke 335/205 1 E 3,467,923 10/1969 Woodhead 335/196 Corporation Ne Yo k, NY, Primary Examiner-Robert K. Schaefer [32] Prio ity May 17,1968 Assistant Examiner-William J. Smith [33] Great B im Attorneys-C, Cornell Remsen, Jr., Walter J. Baum, Percy P. [31] 23493/63 Lantzy, J. Warren Whitesel, Delbert P. Warner and James B. Raden [54] DIAPHRAGM PUSHBUTTON SWITCHES I 22 Claims 15 Drawing ABSTRACT: Pushbutton diaphragm switches are provided. [52] [1.8. CI 200/159, Switch contacts in a hermetically sealed environment are 335/196 energized by changes in magnetic fields caused by motion of a [51] Int. Cl H0lb 13/00 permanent magnet under control of a pushbutton. A pushbut- [50] Field of Search 335/186, ton spring may be dispensed with and magnetic attraction may 196, 205; 200/ l 59 be relied upon to provide the necessary restoring force.

V N i PATENIEU JUN'I 1 Ian SHEET 2 [IF 7 I PATENIEU Jun 1 Ian SHEET 3 [IF 7 PATENIIITEDIJUN nan 3.682, 596

I sum u 0F 7 PATENIEDJUN nan 13,582,596

- amson DIAPHRAGM PUSHBUTTON SWITCHES This invention relates to ON/OFF and changeover switches and in particular but not exclusively to pushbutton switches, and is a modification of the invention relating to electromagnetic relays described in out British Pat. specification No. 1,094,344.

That specification relates to a relay composed essentially of two parts, a contact capsule, and, external to the capsule, an operating winding. The basic form of the relays contact capsule is that of a capsule one wall of which is provided by an inner magnetic member sealed through the central aperture of an annular outer magnetic member, and within the capsule a moving contact provided by a lamina of magnetic material disposed substantially normal to the axis of the outer magnetic member.

For this invention this type of relay has been modified to convert it to a switch employing the same basic form of contact capsule but replacing the operating winding with a magnetic switching member so that the change of magnetic fiux threading the capsule required to actuate the contacts is derived by mechanical means instead of electromagnetically.

According to the invention there is provided a switch including an hermetically sealed contact capsule one wall of which is formed by one or more inner magnetic members extending through and sealed in the central aperture of an annular outer magnetic member, and within the contact capsule one or more moving contacts cooperating with fixed contacts and provided by laminae of magnetic material disposed substantially normal to the axis of the outer magnetic member, the lamina or laminae and the inner and outer magnetic members forming part of a magnetic circuit which includes a permanent magnet and has associated therewith external to the capsule a magnetic switching member movable relative to the outer magnetic member by the movement of which the magnitude of the magnetic flux threading the magnetic circuit may be altered so as to bring the or each lamina into engagement with its cooperating fixed contact.

For a single pole ON/OFF switch the contact capsule may be identical with the construction described in British Pat. specification No. 1,094,334 in which the moving contact is provided by a diaphragm secured at its periphery to the outer magnetic member and the cooperating fixed contact is provided by the inner magnetic member.

The basic form of single pole ON/OFF contact capsule referred to above is susceptible of modification to suit different contact operation requirements. Thus another variant is provided by the use of a fixed contact independent of the inner magnetic member and situated on the opposite side of the diaphragm to that member. Under these circumstances the inner magnetic member need not be electrically insulated from the outer unless both the independent fixed contact and the inner magnetic member are employed as individual contacts in which case the switch becomes a changeover switch. Other variants arise when applying the invention to multiple ON/OFF or multiple changeover switches. Where multiple moving contacts are required, it is not sufficient merely to divide the diaphragm as used in single moving contact switches into the requisite number of sectors, and then have these sectors secured at their curved edges. This is because under these circumstances the advantages of substantially rectilinear relative movement of the contacting surfaces obtained with the diaphragm configuration are lost. To overcome this problem, instead of being secured at its curved edge, each sector is attached to an anchorage post and has an involuted form with a contact area linked to its anchorage area by one or more arms. As with the single make and break and switches the fixed contacts may be situated on one or other or both sides ofthe moving contacts. Where this requires the provision of more than one inner magnetic member these members are electrically insulated from each other but magnetically linked by means of a magnetic yoke.

The above mentioned and other features of the invention will become more apparent and the invention itself will be best understood by reference to the following description of several embodiments of the invention. The description refers to the accompanying drawings in which:

FIG. 1 shows a section through a switch contact capsule,

FIG. 2 shows its diaphragm moving contact,

FIGS. 3, 4, 5, 7 and 9 show sections through alternative contact capsules,

FIG. 6, 8 and 10 show the moving contacts of the capsule shown in FIGS. 5, 7 and 9 respectively, and

FIGS. 11, 12, I3, 14 and 15 show sections through different embodiments of pushbutton switches.

The ensuing description of embodiments of the invention is conveniently divided into two parts; the first part relating to contact capsules in which the switch contacts are housed, and the second part relating to the means by which the contacts of such capsules can be operated from outside the capsule.

The contact capsule illustrated in FIG. I which is one variant of a single ON/OFF contact capsule is built up from a glass-to-metal seal 1 which serves to seal an inner magnetic member 2 inside the central aperture of an annular outer magnetic member 3, thereby both magnetically and electrically insulating the inner magnetic member from the outer. A diaphragm 4 of magnetic material is secured at its periphery to the outer magnetic member so that it just clears the end face of the inner magnetic member which has a shallow hole bored in it to leave an annular contact surface 5. The diaphragm 4 which is shown in section in FIG. 1 and in plan in FIG. 2 is, in its unstressed state, a plane disc having an outer region 6 linked by a number of slender arms 8 with a central region 7 which includes the contact making area. These arms are formed by cutting in the diaphragm three slots 9 having a length much greater than their width and cut in the form of arcs of circles. This symmetrical arrangement serves to increase the resiliency of the diaphragm giving the central region 7 considerable freedom of movement by reducing the stress necessary to distort it, while at the same time ensuring that when attracted towards the inner magnetic member by means of magnetic attraction it is constrained to move substantially rectilinearly into contact with the end surface 5. The capsule is completed by means of a cap 10 which can be conveniently attached to the outer magnetic member by projection welding resulting in a hermetically sealed structure which can have any desired atmosphere sealed within it. The contacts are operated by means of an externally applied magnetic flux threading the inner magnetic member 2, the diaphragm 4, and the outer magnetic member 3. The diaphragm 4 must, of course, be made of a magnetic material such as a nickel-iron alloy, and, in order to present a low resistance path, may be plated with a good conductor such as silver. This may be overplated at least in the contact making region with a layer having good contact properties such as paladium or one of the other noble metals. The cooperating contact surface 5 of the inner magnetic member 2 may be similarly plated. These layers besides improving the electrical contact properties of the contact members also serve to provide the necessary magnetically insulating spacer between them which prevents their magnetic parts from coming into intimate contact with each other. The outer magnetic member 3 may be provided with an internal flange ll of magnetic material which serves to concentrate any magnetic flux threading the diaphragm in its central region 7 so that the gap between the inner magnetic member 2 and the central region 7, and the gap between the central region 7 and the flange II are in series in the magnetic circuit. Under these circumstances any flux in this circuit exerts forces across these gaps which are in parallel, or in other words which are additive. If this flange II is dispersed with the cap 10 is made of magnetic material in order to provide an adequate return path for the flux between the central area of the diaphragm and the outer magnetic member. External connections to the contact capsule are made to the inner magnetic member 2 and to the outer magnetic member 3 or to the cap 10.

FIG. 3 illustrates another variant of the single ON/OFF contact capsule which differs from the first in that an increase of magnetic flux threading the capsule is required to separate the contacts instead of being required to close them, as is the case in the first variant illustrated in FIG. 1. This second variant is identical with the first except in the following respects. Firstly, the seal 1 is not necessarily electrically insulating as the inner magnetic member does not serve as a switch contact, though it still has to be magnetically insulating. Secondly, the cap is dispersed with and its place taken by a different construction consisting of an inner cap member 32 sealed in the central aperture of an annular outer cap member 33 by means of an electrically insulating seal such as a glass-to-metal seal 31. Thirdly, the inner cap member 32 is provided with a precious metal fixed contact surface 35 which is annular and which butts against the central region 7 of the diaphragm 4 slightly distorting it to provide the necessary contact pressure. The term distorting is used here as elsewhere in this specification to denote straining which is within the elastic limit of the material. In the case of the diaphragm such distortion will be confined almost entirely to the arms 8. And fourthly, an insulating washer 36 is provided to prevent the diaphragm from coming into intimate magnetic contact with the inner magnetic member 2. External connections to this switch capsule are made to the inner cap member 32 and to the outer magnetic member 3 or to the outer cap member 33.

A third variant of contact capsule is illustrated in FIG. 4. This variant is a single changeover capsule which incorporates all the features of the first two variants except for the cap 10 the insulating washer 36. In this case, as in the first variant, the seal 1 has to be both magnetically and electrically insulating. External connections to this switch capsule are made to the inner magnetic member 2, to the inner cap member 32, and to the outer magnetic member 3 or to the outer cap member 33.

The fourth, fifth and sixth variants which will now be described are multiple contact versions of the second, first and third variants of contact capsule respectively. In order to demonstrate a variety of multiplicities of contact sets the examples to be described each have a different multiplicity. It should be apparent however that the particular multiplicity chosen for any particular variant is arbitrary, and no special significance should be attached to that choice. Instead of having a single diaphragm as the moving contact, each of the following variants has a number of substantially coplanar laminae having the basic form of sectors, which laid side-byside, form the rough outline ofa disc. In the same way that the diaphragm has a contact making area linked by arms to an outer area by which it is secured, so each lamina has an involute form consisting of a contact area linked by one or more arms to an anchorage area.

The fourth variant of contact capsule, a two-pole ON/OFF switch capsule, is illustrated in FIG. 5, and the arrangement and configuration of its laminae illustrated in FIG. 6. Its construction is identical with that shown in FIG. 3 except that two resilient laminae 54 are substituted for the diaphragm 4 and there are four terminals sealed through the central aperture of the outer cap member 33. Two of these terminals are anchorage posts 59 to which the laminae are secured and the remaining two are fixed contact members 52, each provided with a precious metal fixed contact surface which is annular and which butts against the contact-making region 67 of the lamina 54 slightly distorting it from the flat in order to provide the necessary contact pressure. The involute shape of the laminae is shown in FIG. 6 each lamina consisting of a contact-making area 67 linked by a single area 68 which embraces one side of the lamina to anchorage area 66. FIG. 6 also shows in dotted detail the positions of the anchorage posts 59, the annular contact surfaces ofthe contacts 52 and the inner magnetic member 2 in their relation to the laminae. Since the laminae are substituted for the diaphragm they must also be made of magnetic material, and may also be plated, like the diaphragm, to improve their conductivity and contact properties. External connections to this contact capsule are made to the two anchorage posts 59 and the two fixed contact members 52.

The fifth variant, which is illustrated in FIGS. 7 and 8, is a three-pole ON/OFF contact capsule, and whereas he fourth variant requires an increase of magnetic flux threading the capsule in order to separate the contacts; in this variant an increase of flux serves to bring the contacts together. FIG. 7 shows a section through one of the laminae when it is magnetically energized. This variant can be seen to be the multiple contact version of the first variant described with reference to FIGS. 1 and 2. It is distinguished from that variant in the following respects. The diaphragm is replaced by three laminae 74, each of which in its unstressed state is flat, and consists of a contact area 87 linked by two arms 88 to its anchorage area 86, by which it is secured to one of three anchorage posts 79. The anchorage posts together with three inner magnetic members 72 are sealed by the glass-to-metal seal 1 in the central aperture of the annular outer magnetic member 3. The inner magnetic members 72 like the inner magnetic member 2 in FIG. 1 are formed with annular end faces 75 which provide the fixed contact surfaces and which may be plated in a similar manner to the contact surface 5 to improve their contact properties. Where they project outside the capsule the inner magnetic members 72 are magnetically linked by a magnetic yoke 73 from which they are electrically insulated by means of electrically insulating sleeves 71. In this variant the magnetic circuit which actuates the switch threads the magnetic yoke 73, from which it branches into the inner magnetic members 72, into the laminae 74, and then is reunited in its return path threading the cap 10 and the outer magnetic member 3. External electrical connections to this switch capsule are made to the three anchorage posts 79 and the three inner magnetic members 72.

The sixth variant, which is illustrated in FIGS. 9 and 10, is a four-pole changeover contact capsule which combines the features of the fourth and fifth variants. Each lamina 94, which in its unstressed state is flat, has a contact area 97 linked by two arms 98 to an anchorage area 96. External electrical connections to the switch capsule are made to the four anchorage posts 99, the four inner magnetic members 92 and the four fixed contact members 92.

These contact capsules all possess the feature that they can readily be made in a hermetically sealed form. Although they include in their construction glass-to-metal seals, the construction is such that the seals can be made as one of the first steps of manufacture so that the relatively high temperature involved in their making does not affect such items as the diaphragm or the laminae which can be added at a later stage. The final sealing operation can be the sealing of one metal component to another and can be effected by methods such as projection welding which heats the bulk of the capsule scarcely at all.

The switch capsules described above are readily suited for incorporation in miniature switches since a practical realization of such a capsule need be no larger than 1 cm. in diameter and 0.5 cm. in depth. The preferred embodiments of the present invention are pushbutton switches and four are described with reference to FIGS. 11, 12, 13 and 14 which show arrangements using the first variant of contact capsule. They can of course be modified to suit the other variants of capsule. In each of these embodiments switching is effected by the movement of a permanent magnet relative to the contact capsule thereby changing the reluctance of a magnetic circuit including the magnet and the capsule and hence changing the amount of magnetic flux threading it.

FIG. 11 shows a moving magnet pushbutton switch having a flanged hollow pushbutton 101 which is retained by a cooperating flange 102 on a switch housing member 103 surrounding the contact capsule 104. A cylindrical permanent magnet 105 is secured in the hollow of the pushbutton and is surrounded by a helical compression spring 106 which bears on an insulating washer 107 which surrounds the inner magnetic member 108 of the capsule where it emerges from the capsule. Terminal connections to the switch are shown at 109 and the switch assembly is completed by the attachment of a baseplate 110 to the switch housing member 103.

The pushbutton 101 is made of magnetic material, but the switch housing member 103 is not, so that magnetic flux from the permanent magnet 105 threads the inner and outer magnetic members of the switch capsule 104 and returns to the magnet via the pushbutton 101. The clearance between the magnet and the inner magnetic member is made slightly greater than that between the flange on the pushbutton and the contact capsule, so that the magnet is prevented from coming into intimate contact with the inner magnetic member. The strength of the spring is chosen so that it will overcome the full magnetic force of attraction existing when the pushbutton is fully depressed, so that when released it will spring back of its own accord. The magnetic force of attraction will of course increase as the pushbutton is depressed and so can give rise to a feeling of snap action in operation, which is often desirable in pushbutton switches. A modification of this switch is illustrated in FIG. 12 in which the permanent magnet is not secured to the button but merely held captive by it. The modified pushbutton includes a nonmagnetic flanged tube 111 within which the permanent magnet is permitted a limited amount of free movement in order to provide an enhanced snap action associated with operation of the switch. As before, even when the pushbutton is fully depressed, the clearances may be chosen so as to prevent intimate contact between the magnet 105 and the inner magnetic member 108, and a nonmagnetic washer 112 prevents its direct contact with the magnetic part of the pushbutton. There is now seen to be a gap in the magnetic circuit at each end of the permanent magnet and the dimensions of the switch can be chosen so that when the pushbutton is depressed the magnetic attraction across the gap between the magnet and the inner magnetic member rises to exceed that across the washer 112. When this happens the magnet snaps against the retaining flange of the tube 111. If the dimensions have been correctly chosen, as the pushbutton is released the flange of the tube 111 will carry the magnet away from the inner magnetic member until a point is reached when the attractive force across this widening gap is reduced below that across the gap at the other end of the magnet, whereupon the magnet will snap back to its original position resting against the washer 112.

FIG. 13 illustrates how by means of an extra flange, indicated at 131, on the housing 103 and dished washer 132 the switch can be adapted to have provision for overtravel of the pushbutton allowing it to be depressed further than is required to bring the magnet to its closest approach to the inner magnetic member of the switch capsule.

In the foregoing examples of pushbutton switches although the switch contacts are completely sealed within the contact capsule there is a slot in the side of the pushbutton to accommodate the terminal connection to the inner magnetic member and it may be possible for foreign material to enter the switch through this opening. FIG. 14 shows an alternative construction of pushbutton switch in which the contact capsule 104 is attached to the pushbutton 101 and the permanent magnet 105 is secured to the baseplate 110. With this construction it is possible to fit a gasket 140 between the cooperating flanges of the pushbutton 101 and the housing member 103 so as to seal the interior of the switch from contamination from the outside. This gasket is of course less effective while the pushbutton is depressed. In place of the single compression spring there are two concentric compression springs 141 and 142, which also form the electrical connections to the inner and outer magnetic member of the capsule, and are connected to terminal pins 143 located in insulating sleeves 144 in the baseplate 110. Connection to the inner magnetic member 108 is made via an electrically conductive washer 145. An insulating sleeve 146 around the permanent magnet protects the inner compression spring from an accidental short to the magnet. In distinction from the former pushbutton switches it is the housing member 103 which is made of magnetic material and the pushbutton 101 which is made of nonmagnetic material.

Although the above-described embodiments of pushbutton switches have all been of the type in which operation is effected by the movement ofa permanent magnet relative to the contact capsule so as to alter the reluctance of the magnetic circuit which includes the magnet and the switch capsule, this invention is not limited exclusively to such types. It should be clear that the permanent magnet can be fixed in relation to the contact capsule and can even form part of the capsule, and the reluctance of the circuit altered by the movement of some magnetic part which is not a permanent magnet.

In another form of construction illustrated in FIG. 15 the movement of the pushbutton does not change the reluctance of the magnetic circuit which includes the permanent magnet and the contact capsule, but changes the reluctance of the magnetic shunt path bypassing the capsule.

Referring to FIG. 15 the permanent magnet 105 in this construction is attached to the contact capsule 104 via a disc 151 of magnetic material and an insulating moulding 152 surrounding the inner magnetic member l08.of the capsule 104. The contact capsule is housed within the housing member 103, which is made of magnetically insulating material, and both are attached to the baseplate 110. The opposite end of the permanent magnet fits in a cap 153 of magnetic material which is a sliding fit inside a nylon liner 154 lining the inside of the pushbutton 101. This liner 154 is introduced to reduce the friction between the cap and the pushbutton. The pushbutton, which is made of magnetic material, is formed with a flange 155 which cooperates with a flange formed on the housing member so that the pushbutton is held captive. Underlying this flange 155 is a washer 156 of magnetic material which is normally attracted by the permanent magnet into contact with the disc 151. This discis formed with a radial slot to accommodate the terminal connection 109 to the inner magnetic member and is insulated from that terminal by part of the moulding 152. The washer and the disc together form a mag netic shunt bypassing the contact capsule. When the pushbutton is depressed the reluctance of this shunt path is increased and therefore more flux is diverted into threading the capsule. Provided that a strong enough permanent magnet is used this pushbutton switch does not need a return spring for the pushbutton because there is sufficient magnetic restoring force to cause the pushbutton to rise when it is released. The sole magnetic restoring force is provided by the attraction across the gap between the washer 156 and the disc 151, and therefore, if a return spring is safely to be dispensed with, the permanent magnet has to generate sufflcientmagnetic flux to operate the contact capsule when the pushbutton is fully depressed and still leave sufficient flux threadihg this gap to provide a stronger force' of attraction across it than any counteracting forces. The counteracting forces are those acting on the washer 156 due to the flux threading the contact capsule, and that acting directly on the pushbutton due to any flux threading the gap between the magnet and the top of the pushbutton. This last force is reduced to a minimum by the provision of the cap 153 which diverts the great majority of the flux direct to the sidewalls of the pushbutton.

Although in the foregoing description the method of operation of the switch contacts has been by means of a change of reluctance of a magnetic circuit associated with the magnet and switch capsule, this is not the only method available. An alternative method of switching is possible in which the flux change in the capsule is caused by a change of magnetomotive force in its magnetic circuit. This can be effected, for example, by rotation of the permanent magnet so that its direction of magnetization can either lie in the magnetic circuit thereby giving rise to maximum m.m.f., or across it, in which case the m.m.f. drops to zero.

In the variants of contact capsule described with reference to FIGS. 4 and 5 the periphery of the diaphragm will always be pressed against the outer magnetic member by virtue of the fact that the diaphragm is at all times stressed, consequently in these variants it is not necessary for the periphery of the diaphragm to be positively secured to the outer magnetic member.

It is to be understood that the foregoing description of specific examples of this invention is made by way of example only and is not to be considered as a limitation on its scope.

Iclaim:

l. A switch including a hermetically sealed contact capsule having one wall formed by an inner magnetic member extending through and sealed in the central aperture of an annular outer magnetic member, movable contact within the contact capsule cooperating with a fixed contact, each of the contacts being formed of magnetic material, the movable contacts being disposed substantially normal to the axis of the outer magnetic member, the contacts and the inner and outer-magnetic members forming part of the magnetic circuit, a magnetic switching member formed by a permanent magnet located external to the capsule and a pushbutton member of magnetic material positioned external to the permanent magnet, said switching member being movable relative to the outer magnetic member to alter the magnitude of the magnetic flux threading the magnetic circuit and to bring the movable contact into engagement with the cooperating fixed contact.

2. A switch as claimed in claim I wherein by the movement of the switching member relative to the outer magnetic member in such a way as to increase the magnitude of the magnetic flux threading the magnetic circuit the moving contact is separated from its cooperating fixed contact.

3. A switch as claimed in claim 1 wherein by the movement of the switching member relative to the outer magnetic member in such a way as to increase the magnitude of the magnetic flux threading the magnetic circuit the movable contact is separated from one of a pair of cooperating fixed contacts and is brought into engagement with an associated inner magnetic member which forms the other member of the pair of cooperating fixed contacts.

4. A switch as claimed in claim 1 wherein the movable contact is provided by a diaphragm the central area of which forms its contact making area and which at its periphery is held in contact with the outer magnetic member.

5. A switch as claimed in claim 4 wherein the diaphragm has therein a number of apertures situated between its peripheral and its central contact making areas so formed that their presence reduces the stress necessary to distort the diaphragm.

6. A switch as claimed in claim 5 wherein said apertures are slots.

7. A switch as claimed in claim 5 wherein the apertures are so formed that the central contact making area is linked with its peripheral area by a number of slender arms.

8. A switch as claimed in claim 1, having a plurality of movable contacts each movable contact having an involute form consisting of a contact making area linked by one or more arms to an anchorage area by which it is secured to an anchorage pose sealed through a wall of the contact capsule.

9. A switch as claimed in claim 8 wherein the movable contacts are substantially coplanar.

10. A switch as claimed in claim 1 wherein the inner magnetic member is secured within the central aperture of the outer magnetic member by a glass-to-metal seal.

11. A switch as claimed in claim 1 wherein the movable contact is plated with a layer of a good conductor of electricity.

12. A switch as claimed in claim 1 wherein the contact making area of the moving contact is plated with a layer ofa noble metal.

13. A switch as claimed in claim 1 wherein the contact making area of the fixed contact is plated with a layer of a noble metal.

14. A switch as claimed in claim 1 wherein the contact makingarea of the fixed contact has the form ofa plane annulus.

5. A switch as claimed in claim 1 wherein the magnetic switching member forms part of the magnetic circuit which includes the contacts and the inner and outer magnetic members as well as the permanent magnetic.

16. A switch as claimed in claim 1 wherein the permanent magnet is rigidly attached to the pushbutton.

17. A switch as claimed in claim 1 wherein the permanent magnet is held captive by the pushbutton.

18. A switch as claimed in claim 1 wherein the permanent magnet is rigidly attached to the pushbutton.

19. A switch as claimed in claim 1 wherein the magnetic switching member forms a variable reluctance shunt path bypassing the inner and outer magnetic members.

20. A switch as claimed in claim 19 wherein the outer magnetic member is rigidly attached to the inner magnetic member or members.

21. A switch as claimed in claim 19 wherein the magnetic switching member is actuated by the pushbutton.

22. A pushbutton switch as claimed in claim 21 wherein the pushbutton restoring force is solely derived from magnetic attraction between component parts of the switch. 

1. A switch including a hermetically sealed contact capsule having one wall formed by an inner magnetic member extending through and sealed in the central aperture of an annular outer magnetic member, movable contact within the contact capsule cooperating with a fixed contact, each of the contacts being formed of magnetic material, the movable contacts being disposed substantially normal to the axis of the outer magnetic member, the contacts and the inner and outer magnetic members forming part of the magnetic circuit, a magnetic switching member formed by a permanent magnet located external to the capsule and a pushbutton member of magnetic material positioned external to the permanent magnet, said switching member being movable relative to the outer magnetic member to alter the magnitude of the magnetic flux threading the magnetic circuit and to bring the movable contact into engagement with the cooperating fixed contact.
 2. A switch as claimed in claim 1 wherein by the movement of the switChing member relative to the outer magnetic member in such a way as to increase the magnitude of the magnetic flux threading the magnetic circuit the moving contact is separated from its cooperating fixed contact.
 3. A switch as claimed in claim 1 wherein by the movement of the switching member relative to the outer magnetic member in such a way as to increase the magnitude of the magnetic flux threading the magnetic circuit the movable contact is separated from one of a pair of cooperating fixed contacts and is brought into engagement with an associated inner magnetic member which forms the other member of the pair of cooperating fixed contacts.
 4. A switch as claimed in claim 1 wherein the movable contact is provided by a diaphragm the central area of which forms its contact making area and which at its periphery is held in contact with the outer magnetic member.
 5. A switch as claimed in claim 4 wherein the diaphragm has therein a number of apertures situated between its peripheral and its central contact making areas so formed that their presence reduces the stress necessary to distort the diaphragm.
 6. A switch as claimed in claim 5 wherein said apertures are slots.
 7. A switch as claimed in claim 5 wherein the apertures are so formed that the central contact making area is linked with its peripheral area by a number of slender arms.
 8. A switch as claimed in claim 1, having a plurality of movable contacts each movable contact having an involute form consisting of a contact making area linked by one or more arms to an anchorage area by which it is secured to an anchorage pose sealed through a wall of the contact capsule.
 9. A switch as claimed in claim 8 wherein the movable contacts are substantially coplanar.
 10. A switch as claimed in claim 1 wherein the inner magnetic member is secured within the central aperture of the outer magnetic member by a glass-to-metal seal.
 11. A switch as claimed in claim 1 wherein the movable contact is plated with a layer of a good conductor of electricity.
 12. A switch as claimed in claim 1 wherein the contact making area of the moving contact is plated with a layer of a noble metal.
 13. A switch as claimed in claim 1 wherein the contact making area of the fixed contact is plated with a layer of a noble metal.
 14. A switch as claimed in claim 1 wherein the contact making area of the fixed contact has the form of a plane annulus.
 15. A switch as claimed in claim 1 wherein the magnetic switching member forms part of the magnetic circuit which includes the contacts and the inner and outer magnetic members as well as the permanent magnetic.
 16. A switch as claimed in claim 1 wherein the permanent magnet is rigidly attached to the pushbutton.
 17. A switch as claimed in claim 1 wherein the permanent magnet is held captive by the pushbutton.
 18. A switch as claimed in claim 1 wherein the permanent magnet is rigidly attached to the pushbutton.
 19. A switch as claimed in claim 1 wherein the magnetic switching member forms a variable reluctance shunt path bypassing the inner and outer magnetic members.
 20. A switch as claimed in claim 19 wherein the outer magnetic member is rigidly attached to the inner magnetic member or members.
 21. A switch as claimed in claim 19 wherein the magnetic switching member is actuated by the pushbutton.
 22. A pushbutton switch as claimed in claim 21 wherein the pushbutton restoring force is solely derived from magnetic attraction between component parts of the switch. 